In recent years hydraulic fracturing (commonly referred to as “fracking” or “hydrofracking”) has become a common method for extracting natural gas and other hydrocarbons from compact rock formations that were previously difficult to exploit. The hydraulic fracturing technique requires the injection of a typically water-based fluid (commonly referred to as “fracturing fluid” or “fracking fluid”) into a well that has already been drilled. The fracking fluid initiates fractures in the rock formation and transports proppants, such as sand or ceramic balls, into the formation in order to support the opened fractures to maintain the permeability of the formation.
Gelling agents, such as guar gum, are typically added to the fracking fluid in order to increase the viscosity of the fluid. Guar gum is a high molecular weight polysaccharide produced from guar beans. Guar gum is known to be an effective thickening agent, and a relatively small amount can substantially increase the viscosity of a water-based fracking fluid. The increased viscosity is desirable because it allows the fluid to effectively and efficiently transport the proppant into the fractures in the formation. Once the fracturing operation has been completed, chemical agents commonly referred to as “gel breakers” are injected into the fractures in order to degrade the high molecular weight guar, thereby facilitating recovery of the fracking fluid. The fluid flows back to the surface (consequently, it is commonly referred to as “flowback water” or “flowback fluid”) and is recovered. Flowback water comprises fracking fluid as well as formation water present in the pores of the rock formation.
Although some guar is degraded by the use of gel breakers, the recovered flowback water typically remains contaminated with significant quantities of guar, along with other contaminants. Because guar is a gel-like substance, it can cause significant performance problems with conventional treatment technologies such as membrane separation, coagulation, or flocculation. Synthetic polysaccharides that can be used to replace guar are available, but are also difficult to remove from flowback water. In addition, guar is often crosslinked using borate salts during the fracking process, thereby increasing the difficulty of removing the guar from the flowback water.
The fracking process requires substantial quantities of fracking fluid in order to effectively fracture a rock formation. Thus, fracking operations produce significant quantities of flowback water. Typically, over one million gallons of flowback water are recovered at a drilling site in the first 2 to 3 weeks alone. This flowback water must be recycled, disposed of, or treated and discharged to the environment. Because such large quantities are produced, flowback water would ideally be recycled for use in future fracking operations. However, the used gel present in flowback water can adversely affect the functioning of new gel, thereby necessitating the treatment of flowback water containing used gel before the water can be recycled. Preferably, this treatment would take place in the field near other fracking sites where the treated water could be reused.
Therefore, a need exists in the art for an effective and economical method for treating flowback water contaminated with guar or similar gelling agents. Furthermore, a need exists in the art for a system for treating flowback water that has the capability of treating substantial quantities of flowback water and that can be economically constructed in the field near fracking sites so that the treated water can be recycled for use in fracking operations.